Fifth wheel assemblies for releasably coupling tractors to trailers are well known. Each fifth wheel assembly includes two bearing surfaces; namely, a tractor bearing plate pivotally mounted on the upper rear portion of the tractor, and a trailer bearing plate or bolster plate mounted on the undersurface of the forward portion of the trailer. The tractor bearing plate supports the weight of the trailer resting against it and acts as a surface against which the bolster plate of the trailer rotates as necessary during towing operations. The tractor bearing plate must be suitably lubricated in order to enable the bearing surfaces to safely rotate relative to each other when the wheels of the tractor are turned.
Various tractor bearing plate attachments have been proposed in the past which are designed to obviate the need to repeatedly apply lubricant to the engaged bearing surfaces. For example, U.S. Pat. No. 4,542,912 granted to St. Louis on Sept. 24, 1985 discloses a bearing attachment consisting of an anti-friction polyolefin sheet. U.S. Pat. No. 3,924,909 granted to Kent et al. on Dec. 9, 1975 also discloses a liner of low friction material fastened to the tractor bearing plate and an overlying cover plate for protecting the low friction liner during coupling and uncoupling operations. U.S. Pat. No. 4,752,081, granted to Reeners et al. on June 21, 1988, similarly discloses a low friction plastic covering and a pair of elongate metal plates to prevent the plastic covering from being gouged or torn during the trailer coupling and uncoupling procedure.
The above-noted plastic surfaces designed to provide an ever-lasting lubricant have not been widely adopted in the trucking industry. One of the primary drawbacks of such anti-friction sheets is that they are easily scuffed or torn. Although the protective cover plates prevent accumulation of abrasive residue on the sheet surfaces to a certain degree, the surfaces still become fouled with debris, particularly if the tractor is driven for long distances over gravel logging roads and the like with the trailer detached.
If a tractor bearing plate becomes covered with abrasive residue it should preferably be cleaned and relubricated. However, in practice this is often not done as frequently as necessary in order to maintain the fifth wheel assembly in the optimum working condition. When a trailer is coupled to a tractor bearing plate covered with abrasive residue, the abrasive residue will often gouge the trailer bolster plate over time. This eventually results in the need for expensive repairs since a new bolster plate must then be welded to the undersurface of the trailer carriage.
For various reasons, it is becoming increasingly common in the trucking industry for tractors to be driven with the trailer detached (commonly referred to in the trade as "bob-tailing"). Accordingly, the need has arisen for a removable slip cover shaped to conform to a conventional tractor bearing plate for protecting the lubricated surfaces of the bearing plate from abrasive residue when the tractor is driven with the trailer detached.